class Solution {//leetcode69——x的平方根
public:
    int mySqrt(int x) {
        if(x<1) return 0;
        int left=1,right=x;
        while(left<right){
            long long mid=(right-left+1)/2+left;
            if(mid*mid<=x) left=mid;
            else right=mid-1;
        }
        return left;
    }
};